1. Field of the Invention
The present invention relates to a torque converter used for a power transmission of a vehicle and the like.
2. Description of the Related Art
Conventionally, a torque converter is widely used in such a manner as to be disposed between an engine and a transmission. The above torque converter is of a 3-element type, namely, including a pump impeller, a turbine runner and a stator. More specifically, the above torque converter has a fluid pass construction including an inlet of the pump impeller, an outlet of the pump impeller, an inlet of the turbine runner, an outlet of the turbine runner, an inlet of the stator, and an outlet of the stator. The inlets and the outlets of each of the three elements have fluid pass areas that are substantially common. The fluid pass area is about 23% of an area of a circle defined by an outermost diameter (nominal diameter) of the torque converter.
The above torque converter can absorb and amplify a torque. The thus absorbed torque is commensurate with a work done by a fluid flowing in the fluid pass in the pump impeller. As a criteria, the thus absorbed torque is referred to as a torque capacity. More specifically, a torque capacity factor is defined as an input torque divided by a second power of an input speed {=input torque/(input speed)2}. The torque capacity smaller than its proper value for an engine torque may cause a high engine speed, resulting in a heavy fuel consumption. On the other hand, the torque capacity greater than its proper value for the engine torque may cause a heavy load to the engine. In sum, it is important to provide the torque capacity that is proper for the engine.
Having the fluid pass areas that are substantially “common” among the inlet inlets and the outlets of each of the three elements, the above conventional torque converter is likely to limit its torque capacity. In other words, the torque capacity has its upper limit. Thereby, the thus limited torque capacity cannot be applied to the engine that has high torque. Use of the torque converter having a low torque capacity for the high torque engine, however, may be responsible for the heavy fuel consumption.
Due to the substantially “common” fluid pass areas, enlarging the outermost diameter (nominal diameter) for securing the required torque capacity may involve increased weight, resulting in the heavy fuel consumption and higher cost.
Japanese Patent Unexamined Publication No. Heisei 11 (1999)-063149 (JP 11063149) discloses a torque converter having the following construction for securing the torque capacity factor.
At first, a first area ratio A, a second area ratio B and a third area ratio C are respectively defined as follows. (A) The first area ratio A is an area of an outlet of a turbine runner, divided by an area of a circle defined by an outermost diameter D; the first area ratio A is also an area of an inlet of a stator, divided by the area of the circle defined by the outermost diameter D. (B) The second area ratio B is an area of an outlet of the stator, divided by the area of the circle defined by the outermost diameter D; the second area ratio B is also an area of an inlet of a pump impeller, divided by the area of the circle defined by the outermost diameter D. (C) The third area ratio C is an area of an outlet of the pump impeller, divided by the area of the circle defined by the outermost diameter; the third area ratio C is also an area of an inlet of the turbine runner, divided by the area of the circle defined by the outermost diameter D.
With the above definition, the first area ratio A, the second area ratio B and the third area ratio C provide the following conditions:                (1) The first area ratio A is in a range from 0.24 to 0.31, the second area ratio B is in a range from 0.24 to 0.31, and the third area ratio C is in a range from 0.23 to 0.31, meeting A=B>C.        (2) The first area ratio A is in a range from 0.24 to 0.31, the second area ratio is in a range from 0.23 to 0.31, and the third area ratio is in a range from 0.23 to 0.31, meeting A>B and A>C.        (3) The first area ratio A is in a range from 0.23 to 0.31, the second area ratio B is in a range from 0.24 to 0.31, and the third area ratio C is in a range from 0.23 to 0.31, meeting B>A and B>C.        
By optimizing the area ratios for the fluid pass based on the above conditions, the torque converter according to Japanese Patent Unexamined Publication No. Heisei 11 (1999)-063149 (JP11063149) is supposed to increase the torque capacity.